Refrigerant Subcooling in a Vehicle HVAC System

ABSTRACT

An HVAC system, and a method of operation, for use in a vehicle is disclosed. The HVAC system may comprise: an evaporator having a drain that receives condensate dripping from the evaporator; a refrigerant compressor that receives a refrigerant from the evaporator and compresses the refrigerant; a condenser that receives the refrigerant from the compressor; and a condensate-to-refrigerant heat exchanger that receives the refrigerant from the condenser and the condensate from the drain, whereby the condensate absorbs heat from the refrigerant as the condensate flows through the condensate-to-refrigerant heat exchanger.

BACKGROUND OF INVENTION

The present invention relates generally to heating, ventilation and air conditioning (HVAC) systems for use in vehicles, and more particularly to the air conditioning portion of the HVAC systems.

There is a significant drive to improve the fuel economy of automotive vehicles. One vehicle operation that reduces fuel economy is air conditioning because it consumes a significant amount of energy when operating. Thus, it is desirable to provide an air conditioning system for a vehicle that operates as efficiently as is practicable while minimizing the cost of the air conditioning system.

SUMMARY OF INVENTION

An embodiment contemplates an HVAC system for use in a vehicle comprising: an evaporator having a drain that receives condensate dripping from the evaporator; a refrigerant compressor that receives a refrigerant from the evaporator and compresses the refrigerant; a condenser that receives the refrigerant from the compressor; and a condensate-to-refrigerant heat exchanger that receives the refrigerant from the condenser and the condensate from the drain, whereby the condensate absorbs heat from the refrigerant as the condensate flows through the condensate-to-refrigerant heat exchanger.

An embodiment contemplates a method of operating an HVAC system in a vehicle, the method comprising the steps of: directing air and a refrigerant through an evaporator to cause the refrigerant to absorb heat from the air; directing condensate from the evaporator through an evaporator drain to a condensate-to-refrigerant heat exchanger; compressing the refrigerant; directing the refrigerant through an expansion device; and directing the refrigerant through the condensate-to-refrigerant heat exchanger after the refrigerant is compressed and before the refrigerant is directed through the expansion device to thereby cause the condensate to absorb heat from the refrigerant.

An advantage of an embodiment is that an air conditioning portion of a vehicle HVAC system may operate more efficiently by increasing refrigerant subcooling using cold condensate produced by an evaporator module to provide increased cooling of the refrigerant.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an HVAC system for a vehicle.

FIG. 2 is a schematic diagram of a cross section of a condensate-to-refrigerant heat exchanger.

DETAILED DESCRIPTION

FIG. 1 illustrates an HVAC system, indicated generally at 22. The HVAC system 22 includes an HVAC module 26 (a portion of which is shown), which includes a blower 28 for forcing air through the HVAC module 26 and an evaporator 30, which receives cooled refrigerant from a refrigerant portion 32 of the HVAC system 22.

The refrigerant portion 32 of the HVAC system 22 also includes a compressor 36, a refrigerant line 34 that directs refrigerant from the evaporator 30 to the compressor 36, a condenser 40, and a refrigerant line 38 that directs refrigerant from the compressor 36 to the condenser 40. The refrigerant portion 32 also includes a condensate-to-refrigerant heat exchanger 44, a refrigerant line 42 that directs the refrigerant from the condenser 40 to the condensate-to-refrigerant heat exchanger 44, an expansion device 46, a refrigerant line 48 that directs refrigerant from the heat exchanger 44 to the expansion device 46, and a refrigerant line 50 that directs refrigerant from the expansion device 46 to the evaporator 30 to complete a refrigerant loop. The expansion device 46 may be, for example, a thermostatic expansion valve, an orifice tube, or a pressure regulator.

The evaporator 30 includes a drain 52. A condensate drain line 54 directs condensate from the drain 52 to an inlet 56 to the condensate-to-refrigerant heat exchanger 44. Another condensate drain line 58 directs condensate from the heat exchanger 44 to atmosphere (i.e., out onto the ground). The condensate-to-refrigerant heat exchanger 44 is a liquid-to-liquid heat exchanger and may take different forms known to those skilled in the art.

FIG. 2 illustrates an example of a type of heat exchanger that may be employed as the condensate-to-refrigerant heat exchanger 44. For this heat exchanger 44, the condensate is directed through a central conduit 62, with the refrigerant directed through an outer, concentric conduit 64. The heat transfer, then, occurs through a wall 66 between the central conduit 62 and the outer, concentric conduit 64.

The operation of the HVAC system 22 will now be discussed relative to FIGS. 1 and 2. When operating a vehicle in hot ambient conditions, the refrigerant portion 32 of the HVAC system 22 is used to cool a passenger compartment of the vehicle. The compressor 36 is activated, compressing refrigerant and pushing it into the condenser 40. As air flows through the condenser 40, heat is removed from the refrigerant, which changes phase from a vapor to a liquid. The refrigerant then flows through the condensate-to-refrigerant heat exchanger 44 and to the expansion device 46. Initially, at air conditioning start-up, there may be little or no condensate flowing through the heat exchanger 44, so initially there may be no heat exchange occurring in the heat exchanger 44. The liquid refrigerant, at high pressure, then flows through the expansion device 46. The expansion device 46 causes the pressure and temperature of the refrigerant to drop, and the refrigerant is then directed through the evaporator 30.

Air flowing through the evaporator 30, forced through by the blower 28, is conditioned for both temperature and humidity. That is, as the air flows through the evaporator 30, the refrigerant flowing through the evaporator absorbs heat from the air—the air temperature is lowered below its dew point, causing moisture in the air to condense out. This condensate produced by the evaporator 30 is collected and directed from the drain 52 through the condensate drain line 54 into the condensate-to-refrigerant heat exchanger.

As the condensate flows through the heat exchanger 44, the cold condensate absorbs heat from the refrigerant before the condensate is discharged, via condensate line 58, to atmosphere (i.e., allowed to flow out onto the ground). The refrigerant flowing through the heat exchanger 44 may be mostly or all in a liquid state, so the heat exchanger 44 may operate as a liquid-to-liquid heat exchanger. By further cooling (subcooling) the refrigerant after it leaves the condenser 40, improved cooling of the air flowing through the evaporator 30 is achieved.

The condensate flow may be passive, that is, employing gravity to cause the flow of the condensate. In such a configuration, the condensate inlet 56 to the condensate-to-refrigerant heat exchanger 44 is at a lower elevation than the drain 52. A condensate outlet 68 from the condensate-to-refrigerant heat exchanger 44 may be at the same or a lower level than the inlet 56 in order to further encourage free flow of the condensate. Alternatively, some type of pump or other means may be used to cause flow of the condensate, if so desired.

As another alternative, the condensate drain line 54, condensate line 58 and central conduit 62 may essentially be a single line through which the condensate flows, with the outer concentric conduit for the refrigerant encircling a portion of this single line.

While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims. 

1. An HVAC system for use in a vehicle comprising: an evaporator having a drain configured to receive condensate that drips from the evaporator; a refrigerant compressor configured to receive a refrigerant from the evaporator and compresses the refrigerant; a condenser configured to receive the refrigerant from the compressor; and a condensate-to-refrigerant heat exchanger configured to receive the refrigerant from the condenser and the condensate from the drain, whereby the condensate absorbs heat from the refrigerant as the condensate flows through the condensate-to-refrigerant heat exchanger.
 2. The HVAC system of claim 1 wherein the condensate-to-refrigerant heat exchanger includes a central conduit through which one of the refrigerant and the condensate is directed and an outer concentric conduit surrounding the central conduit through which the other of the refrigerant and the condensate is directed.
 3. The HVAC system of claim 2 wherein the central conduit is configured to receive the condensate and the outer concentric conduit is configured to receive the refrigerant.
 4. The HVAC system of claim 1 wherein the condensate-to-refrigerant heat exchanger includes a condensate inlet, and the condensate inlet is at a lower elevation than the drain.
 5. The HVAC system of claim 4 wherein the condensate-to-refrigerant heat exchanger includes a condensate outlet, and the condensate outlet is at a lower elevation than the condensate inlet.
 6. The HVAC system of claim 1 further including an expansion device configured to receive the refrigerant from the condensate-to-refrigerant heat exchanger.
 7. A method of operating an HVAC system in a vehicle, the method comprising the steps of: (a) directing air and a refrigerant through an evaporator to cause the refrigerant to absorb heat from the air; (b) directing condensate from the evaporator through an evaporator drain to a condensate-to-refrigerant heat exchanger; (c) compressing the refrigerant; (d) directing the refrigerant through an expansion device; and (e) directing the refrigerant through the condensate-to-refrigerant heat exchanger after the refrigerant is compressed and before the refrigerant is directed through the expansion device to thereby cause the condensate to absorb heat from the refrigerant.
 8. The method of claim 7 including step (f) directing the refrigerant through a condenser to remove heat from the refrigerant, and wherein step (e) is further defined by directing the refrigerant through the condensate-to-refrigerant heat exchanger after the refrigerant leaves the condenser and before the refrigerant is directed through the expansion device.
 9. The method of claim 7 wherein step (b) is further defined by directing the condensate through a central conduit in the condensate-to-refrigerant heat exchanger, and step (e) is further defined by directing the refrigerant through an outer concentric conduit surrounding the central conduit in the condensate-to-refrigerant heat exchanger.
 10. The method of claim 7 including step (f) directing the condensate from an outlet of the condensate-to-refrigerant heat exchanger to atmosphere.
 11. The method of claim 7 wherein step (b) is further defined by locating the condensate-to-refrigerant heat exchanger at a level below the evaporator drain to thereby employ gravity to cause the condensate to move from the evaporator drain to the condensate-to-refrigerant heat exchanger. 